1. Field of the Invention
The present invention relates to an organic light emitting display device and a method of driving the same.
2. Description of Related Art
Various types of flat panel display devices have reduced weight and volume than those of cathode ray tube display devices. The flat panel display devices include liquid crystal display devices, field emission display devices, plasma display devices, organic light emitting display devices, and the like.
Among these flat panel display devices, the organic light emitting display device displays images by using organic light emitting diodes that emit light through recombination of electrons and holes. The organic light emitting display device has a fast response time and is driven with low power consumption.
An organic light emitting display device displays an image by using pixels arranged in a matrix form. Here, each of the pixels includes an organic light emitting diode and a driving transistor that controls an amount of current supplied to the organic light emitting diode.
An operation of the organic light emitting display device will be described. A voltage corresponding to a data signal is first charged into a storage capacitor coupled to a driving transistor. The driving transistor controls an amount of current supplied to an organic light emitting diode, corresponding to the voltage charged into the storage capacitor. Then, the organic light emitting diode emits light of red, green or blue having a luminance corresponding to the amount of current supplied from the driving transistor.
However, in a conventional organic light emitting display device, the threshold voltages and mobilities of driving transistors for pixels may be unequal due to process deviation. If the threshold voltages and mobilities of the driving transistors for the pixels are unequal, the pixels generate lights having different luminances, corresponding to the same data signal. Accordingly, an image having a desired luminance may not be displayed by the pixels.
In order to solve such a problem, a circuit that compensates for the threshold voltage of a driving transistor may be added to each pixel. However, the circuit added to each of the pixels does not compensate for the mobility of the driving transistor.
As time elapses, an organic light emitting diode is degraded, and therefore, an image having a desired luminance may not be displayed. Practically, as the organic light emitting diode is degraded, the luminance of light generated by the organic light emitting diode gradually becomes lower corresponding to the same data signal.